Power transmission belts comprising an elastomeric body reinforced with one or more helical winds of a cord which functions as a tension member such as fiber glass strand, are well known in the art. Some belts also include lateral members to provide lateral stiffness to the belt while permitting longitudinal flexibility thereof when used to transmit power especially in variable pulley drives in which the belt performs its power transmission function by engaging the pulley flanges with its edges. In the absence of the stiffeners, belts sag, become arched and distorted. This is undesirable and is to be avoided. Examples of belts with lateral stiffening are described in U.S. patents to Unger and Redmond U.S. Pat. Nos. 2,189,049 and 3,772,929, respectively.